Refrigerating system including hot gas defrost means



No 29, 19 0 v c. J. NONOMAQUE 2,961,848

REFRIGERATING SYSTEM INCLUDING HOT GAS DEFROST MEANS Filed Oct. 2, 1959I I I ISM I I I I INVENTOR CLYDE :r NONOMAQUE H I S ATTORNEY aren't g A2,961,848 1C6 Paifented Nov. 2

REFRIGERATING SYSTEM INCLUDING HOT GAS DEFROST MEANS Filed on. 2, 1959,set. No. 844,116

1 Claim. c1. 62-278) The present invention relates'to' refrigeratingapparatus and is more particularly .concerned'with a refrigeratingsystem including a hot gas defrost circuit'for warming the evaporatorcomponent of the system to defrosting temperatures; T I

In my copending application S.N; 698,462 filed November'25, 1957, nowPatent No. 2,928,256and assigned to the same assignee as the presentinvention, there is described 'and'claimed' a refrigerating systemincluding an auxiliary hot gas defrosting circuit for'quickly andeffectively defrosting the evaporator component of the refrigerantsystem by means of hot compressed refrigerant.

The refrigerant system described in my cop'ending application preferablycomprises a hermetic compressor, a condenser, a' fixed flow restrictorand "an evaporator connected to 'form'a series-flow normal refrigeratingcircuit in which the refrigerant passing through the hermetic casingcools the motoretnployed for'driving the compressor. For the purpose ofperiodically raisingthe evaporator to defrost temperatures by means ofhot com pressed refrigerant from the compressor, there isfprovided anauxiliary circuit connected between the high and low pressure sides ofthe normal refrigerating circuit and in parallel with at least that partof the normal refrigerating circuit including the fixed flow restrictorand the evaporator. Thisauxiliary circuit includes a deffost portion inheat exchange with the evaporator so that upon opening of a normallyclosed valve in the auxiliary circuit, hot compressed'refrigerant willflow through the defrost portion of the auxiliary circuit in heatingrelation with the evaporator where condensation of refrigerant in thedefrosting portion quickly and effectively warms the evaporator todefrosting temperatures. lThB refrigerant condensed in the defrostportion then passes back to the compressor case where it producesrefrigeration and increases the load on the refrigerant cooledcompressor motor, causing the input watts to the motor to increase andthereby providing additional energy in the form of heat for defrostingoperations.

During the defrost operation of the refrigerating systemtdescribed in myaforementioned application, the refrigeration taking place in thehermetic casing cools the lubricating oil contained therein and sincethe solubility of the refrigerant in the oil increases with decreasingtemperatures, additional refrigerant is dissolved in the oil during thedefrost cycle. In some cases, as with the more oil-soluble refrigerantdichlorodifluoromethane, hereinafter referred to as R-l2, a substantialportion of the total refrigerant charge is absorbed into the oil in thecompressor case. When the defrost function is terminated and the systemis returned to the normal refrigerating operation, the absorbedrefrigerant slowly evolves from the oil, the rate of evolution dependingupon the rate at which the compressor case returns to normal operatingtemperatures. While this delay in the liberation of the refrigerant fromthe foil does .not adversely affect the over-all operation of a systemwhich is defrosted only two or three times per day, systems comprisingevaporators which require a' more frequent defrost, as for example onceeach hour, may be adversely affected since a recovery delay of only afew minutes will cause such systems to operate at higher averageoperating temperatures and longer running times.

It is therefore an object of the present invention to provide arefrigerating system including a hot gas auxiliary defrost circuitcharacterized by a rapid recovery from defrost operation to normalrefrigerating operation. Another object of the present invention is toprovide a refrigerating system including a hot gas or auxiliary defrostcircuit which is particularly adapted for the frequent defrosting of alow mass evaporator component of the system.

A more specific object of the invention is to provide a defrostingrefrigerating system of the above type including a refrigerant componentof limited solubility in oil which will quickly return from the defrostcircuit to the evaporator during a refrigerating cycle following defrostand means in the hot gas defrost or auxiliary defiost circuit forlimiting the flow rate of that refrigerant component to preventexcessive increases in the case pressures and input watts to thecompressor motor during defrost operation of the system.

In carrying out the objects of the present invention there is provided adefrostable refrigerating system comprising an evaporator structureincluding an evaporator passage and a defrost passage in heat exchangewith the evaporator passage. For the purpose of supplying refrigerant tothe evaporator passage there is provided a hermetic compressor unitincluding a sealed casing and a compressor and a motor for driving thecompressor disposed within the casing. The casing contains a supply oflubricating oil for lubricating the compressor and motor. The systemalso includes a condenser and a capillary flow restrictor and conduitmeans connecting the compressor, condenser, capillary flow restrictor,evaporator passage and casing in a series-flow normal refrigeratingci'rcuit whereby'the compressor withdraws lower pressure refrigerantfrom the evaporator through the casing and discharges high pressurerefrigerant to the condenser. By this arrangement, the motor is cooledby the low pressure refrigerant in the casing. For periodicallyintroducing hot compressed refrigerant into the defrost passage in orderto raise the evaporator structure to defrosting temperatures, there isprovided an auxiliary circuit including a hot gas conduit connecting theinlet end of the defrost passage to the refrigerating circuit betweenthe compressor and the flow restrictor and a second conduit including aflow restricting means connecting the outlet end of the defrost passageto the refrigerating circuit between the evaporator passage and thecompressor. A normally closed valve in the auxiliary circuit controlsthe flow of compressed refrigerant to that circuit while the flowrestricting means between the defrost passage and the compressorrestricts the flow of refrigerant to the compressor in order to maintainthe refrigerant in the defrost passage at condensing pressure conditionswhen the valve is opened for defrost operation of the system. To providea quick recovery of the system from defrost operation to normalrefrigerating operation following a defrost period, the system ischarged with a refrigerant mixture including a refrigerant component,such as monochlorodifiuoromethane hereinafter referred to as R-22 havinga relatively low solubility in oil. In order to limit the pressureincreases within the compressor case and hence limit the input watts tothe motor resulting from the presence of the more volatile and lesssoluble refrigerant component, means in the form of a heat exchange between the auxiliary circuit conduit leading to the defrost passage andthe auxiliary circuit flow restricting means is provided. This heatexchange prevents excessive flow of condensed refrigerant from thedefrost passage to the hermetic casing during defrost operation.

For a better understanding of the invention reference may be had to theaccompanying drawing in which the single figure is a diagrammaticillustration of a refrigerating system embodying the features of thepresent invention.

With reference to the drawing there is illustrated a preferredembodiment of the invention comprising a hermetic motor-compressor unit1, a condenser 2, a fixed flow restrictor 3, preferably of the capillarytube type, a cooling or evaporator unit or structure 4 including anevaporator passage 6 and a suction line 5. Preferably, in accordancewith the usual practice, the suction line 5 is in heat exchange with aportion of the flow restrictor 3 as indicated by the numeral 8. Theevaporator structure 4 is illustrated as a double tube extrusionincluding the evaporator passage or circuit 6 and a defrost gas passage9. Also, as part of the evaporator structure there may be provided anaccumulator 7 arranged in the usual manner at the outlets end of theevaporator circuit 6.

The motor compressor unit 1 comprises a motor 10 for driving acompressor 11, the two being sealed in 21 hermetic casing 12. A body ofoil 14 is provided in the lower portion of the casing 12 and iscirculated within the casing by means of an oil pump (not shown) forlubricating the compressor and motor. The suction line 5 is connected tothe case 12 so that the case is part of the low pressure side of thenormal refrigerating system and is therefore filled with low pressurerefrigerant in cooling contact with the motor 10. The compressor 11having its inlet 15 communicating with the interior of the case 12withdraws low pressure refrigerant from the case 12 and discharges highpressure refrigerant directly through a discharge line 16 into thecondenser 2. Thus the compressor, condenser, capillary flow restrictor,evaporator passage and hermetic casing are connected in a series-flowrefrigerating circuit with the evaporator passage 6, the accumulator 7and the case 12 forming the low pressure side of the normalrefrigerating circuit while the compressor 11 and the condenser 2comprise the high pressure side.

It will be understood, of course, that in a typical application of arefrigeration system of this type, the evaporator structure 4 is placedin a cabinet (not shown) which is to be cooled while the condenser 2 isplaced in the ambient atmosphere. During the normal operation of therefrigeration system thus far described, the refrigerant flow pathduring the normal refrigeration cycle is that indicated by the solidarrows in Figure 1. The motor compressor unit 1 withdraws vaporizedrefrigerant from the accumulator 7, or from the evaporator passage 6 ifthe accumulator as a separate component is not employed, and thiswithdrawn refrigerant passes through the suction line 5 and flows intothe casing 12. Compressed refrigerant discharged in the gaseous statefrom the compressor flows into the condenser 2 where it is liquified.The liquified refrigerant flows through capillary flow restrictor 3 intothe evaporator passage 6 where, at a lower pressure, it is vaporized bythe absorption of heat from the cabinet to cool the contents of thecabinet. Any liquid refrigerant not evaporated in the evaporator passagecollects in the accumulator 7, the connection between the accumulator 7and the suction line 5 being such that only gaseous refrigerant iswithdrawn from the accumulator through the suction line during normalrefrigerating operation of the system.

For the purpose of defrosting the evaporator structure, there isprovided an auxiliary defrost circuit which is connected to the normalrefrigerating circuit in parallel relationship with the evaporatorpassage 6, the accumulator 7 and the capillary flow restrictor 3 so thatit forms a heating or defrost circuit for circulation of hot com pressedrefrigerant gas from the compressor through the defrost passage 9 forthe purpose of warming the evaporator structure 4 to defrostingtemperatures.

In the illustrated embodiment of the invention, the inlet end 19 of thisauxiliary circuit is connected to the discharge line 16 leading from thecompressor to the condenser 2 and normally closed valve 20 is providedfor permitting flow of refrigerant through the auxiliary circuit 18during defrost. The conduit 19 is connected to the defrost passage 9which has a portion in heat exchange with the accumulator 7 and anotherportion in heat exchange with the evaporator passage 6. The outlet endof the defrost passage 9 is connected by a restrictor tube 25 to thesuction line 5 as indicated by the numeral 24.

The system as thus far described is constructed in accordance with theteachings of the aforementioned Nonomaque application. Also, inaccordance with the teachings of that application, the restrictor tube25 has a lower flow restriction than the capillary tube 3 but providessufiicient restriction to the flow of refrigerant through that auxiliarycircuit to maintain the compressed refrigerant gas in the defrostpassage 9 at condensing pressures during defrost operation of thesystem. When defrosting of the evaporator structure 4 is required, thevalve 20 is opened with the result that, due to the pressuredifferential and temperature conditions existing in the system uponopening of the valve 20, substantially all of the refrigerant withdrawnfrom the accumulator 7 by the compressor unit 1 flows from thecompressor through the auxiliary circuit as indicated by the brokenarrows instead of the normal refrigerating circuit. In the defrostpassage, which corresponds to the condenser component of a refrigeratingcircuit, the hot compressed refrigerant condenses; the liberated heatserving to melt the frost accumulated on the evaporator structure 4.This condensed refrigerant then passes through the restrictor 25 andreturns as a liquid or liquid-gas mixture to the compressor case 12which functions as the evaporator on defrost. Also, during defrostoperation, refrigerant stored in the evaporator or condenser componentof the normal refrigerating circuit is transferred to the defrostcircuit. This transfer of most of the refrigerant charge to the defrostcircuit and particularly to the compressor case 12, increases the caseor low side pressure of the system so that a greater load is placed onthe motor causing the input watts to the motor to increase even thoughthe case and motor are cooled to a lower temperature during the defrostcycle. The increased heat output of the motor resulting from the higherinput wattage is absorbed by the refrigerant in cooling relationshipwith the motor and is transferred by the circulating refrigerant to thedefrost passage 9 for defrosting of the evaporator structure. Whendefrosting of the evaporator unit is completed, closing of valve 20restores the system to normal refrigerating operation wherein anyrefrigerant dissolved in the oil is liberated as this oil becomes warmerand the case pressure decreases.

Refrigerating systems employing the above-described defrost principle ofoperation have been found to be most satisfactory for defrostingevaporators of high thermal mass particularly when the defrost operationis initiated only a few, for example, one or two times per day since afew minutes delay in the liberation of dissolved refrigerant does notmaterially affect the total refrigerating operation of the system.

However, with systems including evaporators which require frequentdefrosting so that the accumulation of frost which must be removedduring each defrost period is small or with low mass evaporators inwhich the major portion of the evaporator is quickly warmed todefrosting temperatures, any substantial delay in the return of thesystem to normal refrigerating operating temperatures is significant andcan result in higher average operating temperatures for the system andincreased running time. For

example, the 'case of household refrigerators cooled by a forced aircooling system in which air is blown over a low mass evaporator thatmust be kept relatively free of frost collections to facilitateefficient heat removal from the circulating air, frequent defrosting, asfor example once per hour, is required for efficient heat transferbetween the evaporator and the circulating air. A delay of only a fewminutes in the recovery of the system to normal refrigerating operatingtemperatures decreases the total refrigerating period between defrostsand will thus cause significant increases in the average evaporatortemperature and in the total running time for the system.

In accordance with the present invention, the delay in returning thesystem to normal operation temperatures is substantially decreased byemploying as the refrigerant charge for the system a refrigerant mixturecontaining a minor proportion of a refrigerant more volatile and lessoil soluble than the principal constituent of the mixture. Preferably,there is employed a mixture of R-12 and R-22. The presence of smallpercentages of R-22 has been found to exhibit the ability to return thesystem to normal temperatures much more rapidly than is possible withR-l2 alone. In general, a refrigerant mixture containing about 15% byweight of R-22 and about 85% by weight of R-12 is particularlysatisfactory. However, larger proportions of R-22, up to about 35% canbe employed in the practice of the present invention.

The principal reason that R-22 in the indicated amounts minimizes thedelay in the recovery of the refrigerating operation of the system isdue to the fact that R-22 is considerably less soluble in oil than R-l2and also evolves more rapidly from the oil and is returned more quicklyto the evaporator as the oil becomes warmer following a defrost cyclethereby producing a much faster return of the system to normalrefrigerating temperatures. The presence of the R-22 also results in anincrease in capacity of the refrigerating and defrosting systems andthis increase can be controlled by the quantity of R-22 added althoughit is generally desirable to limit the amount of R-22 to a minimum so asnot to overload the compressor motor.

It has further been found that while the addition of the more volatileR-22 to the refrigerant charge provides the desirable function ofreturning the system to normal refrigerating operating temperatures at amuch faster rateor in a much shorter time than is possible with the moreoil soluble R-12, its presence in the system during the defrost cyclemay result in such a rapid increase in the low side or case pressure andhence the input watts to the compressor motor during the defrost cyclethat the usual temperature responsive overload protection provided forthe compressor motor may trip before the defrost operation is complete.In other words, with the more volatile R-22 present in the system, thepressure changes are much greater than with R-12 alone and thesepressure changes are particularly evident as the refrigerant charge istransferred to the compressor case during the initial stages of thedefrost cycle following the opening of the valve 20.

Therefore, in accordance with a further feature of the presentinvention, the system is so constructed as to control this pressure riseand the corresponding increase in the input motor watts. This isaccomplished by heat exchanging the hot gas line 19 with the flowrestrictor 25 in the auxiliary or defrost circuit as indicated by thenumeral 28 in the accompanying drawing. From a consideration of thesystem shown in the accompanying drawing, it will be seen that this heatexchange is effective or comes into operation only during the defrostcycle. When the valve 20 is opened, the lesser total restriction of theauxiliary or defrost circuit as compared with the normal orrefrigerating circuit, causes the refrigerant to flow through theconduit 19 and into the defrost passage 9 wherein it heats theevaporator or refrigerant passage 6 to defrosting temperatures. At thesame time the accumulator 7 is also warmed so that any refrigerantstored therein tends to flowthrough the suction line 5 into thecompressor case 12. The hot gas condensing 'in the defrost passage 9returns as a liquid through the flow-res s'trict'ing means 25 to thecompressor case 12. By providing the heat exchange 28 between the flowrestricting means 25 and the hot gas conduit 19, the, cool liquid in theflow restricting means 25 removes a portion of the heat from the gasflowing through the line 19 which slows the temperature and pressurerise in the defrost passage 9 thus in turn slowing the return flowthrough the flow restricting means 25. In addition, this slower increasein the temperature of the defrost passage 9 decreases the rate oftransfer of accumulated refrigerant in the accumulator 7 to thecompressor case. Thus by the heat exchange 28 a rapid increase in thecase pressure and an overloading of the compressor motor is avoided.

It will be observed that while the net result of the heat exchange 28 isto decrease the rate of fiow of refrigerant through the auxiliarycircuit and back to the compressor case 12., the use of a smaller ormore restrictive flow restrictor means 25 in place of the heat exchange28 to obtain such a decreased flow rate would not be satisfactory. Whilethe use of greater fiow restricting means in the auxiliary circuit woulddecrease the rate of flow to the compressor case, it would also increasethe pressure conditions within the defrost passage 9 and also upset thepressure conditions existing during defrost between the auxiliary ordefrost circuit and the normal refrigerating circuit which is also opento the compressor or interconnected therewith during defrost operation.This would result in an increase in the amount of refrigerant flowingthrough the normal circuit during defrost operation of the system andtherefore an excessive cooling action in the evaporator passage 6 sothat difficulty would be encountered in defrosting all or part of theevaporator structure, particularly the portions thereof near the outletend of the capillary flow restrictor 3. I

While there has been shown and described a particular embodiment of thepresent invention, it is to be understood that the the invention is notlimited to the particular form and is intended by the appended claim tocover all modifications within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

A defrostable refrigerating system comprising an evaporator structureincluding an evaporator passage and a defrost passage in heat exchangewith said evaporator passage, a hermetic compressor unit including asealed casing and a compressor and a motor for driving said compressordisposed within said casing, said compressor having an inlet portcommunicating with the interior of said casing, a condenser and acapillary flow restrictor, conduit means connecting said compressor,condenser, capillary flow restrictor, evaporator passage, and casing inclosed series-flow refrigerating circuit whereby said compressorwithdraws low pressure refrigerant from said casing and discharges highpressure refrigerant to said condenser, a charge of lubricating oil insaid case, a refrigerant charge in said system comprising a mixture ofdichlonodifluoromethane and up to 35% by weight ofmonochlorodifluoromethane, said motor and oil being cooled by lowpressure refrigerant in said casing, and means for periodicallyintroducing hot compressed refrigerant into said defrost passage toraise said evaporator structure to defrosting temperatures comprising anaux iliary circuit including said defrost passage, a hot gas conduitconnecting the inlet end of said defrost passage to said refrigerantcircuit between said compressor and said capillary flow restrictor andmeans including a fixed flow restricting means connecting the outlet endof said auxiliary circuit to said refrigerant circuit between saidevaporator passage and said compressor, said auxiliary circuit includinga normally closed valve for controlling '7 the flow of'compressedrefrigerant through said auxiliary circuit, said flow restricting meansrestricting the flow of refrigerant to said compressor thereby tomaintain refrigerant in said defrost passage at condensing pressureconditions when said valve is open, said auxiliary circuit conduit beingin heat exchange with said auxiliary circuit flow restricting means toprevent excessive flow of condensed refrigerant to said casing when saidvalve is open.

References Cited in the file of this patent UNITED STATES PATENTS

